Examining the effect of spontaneous combustion on vegetation restoration at coal waste dumps after reclamation: Taking Medicago sativa L. (alfalfa) as an indicator.

The Spontaneous combustion problem poses a significant threat to the coal waste dumps after reclamation. Spontaneous combustion alters the soil environment and further affects vegetation growth. Therefore, it is essential to understand the response of vegetation and soil to spontaneous combustion for ensuring vegetation restoration. Here, taking the reclaimed plant type, Medicago sativa L. (alfalfa), as an indicator, this study carried out a field survey in a typical spontaneous combustion area (study area) of a coal waste dump after reclamation. A total of 41 soil and 70 vegetation sampling points were investigated in the field survey, including soil environmental factors (soil temperature, ST; soil water content, SWC; soil organic carbon, SOC; total nitrogen, TN; available phosphorus, AP; available potassium, AK; bulk density, BD; pH) and alfalfa growth indicator (above-ground biomass, AGB). The spatial variation of alfalfa AGB reached 69.9 %, and all soil environmental factors showed moderate variation (12.28-35.03 %) except for BD and pH. ST was found to have a strong explanatory ability on the variation of AGB in the entire study area (q = 0.62, p < 0.01), but the ability weakened with the improvement of the health grades of alfalfa (Grades A, B, C, and D). From Grade D to Grade A, the q-value gradually reduced from 0.71 (p < 0.01) to 0.05 (no significance). The interaction effects of soil environmental factors showed mostly bilinear and non-linear enhancement. In regions with severe vegetation degradation (Grade C and Grade D of alfalfa), the interaction of ST with BD, AP, AK, and TN played a dominant role in the spatial variation of alfalfa AGB (44.8-86.15 %). However, in the regions of Grade A and Grade B, the spatial variation of alfalfa AGB was mainly affected by the interaction effects of AK, TN, AP, and SOC (60.13-84.77 %). As a simple analysis method, Geodetector can help researchers to better understand the complex response mechanism of vegetation-soil under spontaneous combustion of coal waste dump. This study provides a theoretical reference for vegetation restoration of coal waste dumps.